[Building Sakai] Cleanup users' subscriptions when they are not provided anymore

[Jean-Francois Leveque]

Hi all,

My request is about live external/provided users. In my case, they come 
from LDAP.

In the past, they were provided and added as participants to sites and 
their own MyWorkspace if they logged in.

Now they are not provided anymore but Sakai logs errors when loading the 
site they were subscribed to, such as :
org.sakaiproject.site.util.SiteParticipantHelper - 
SiteParticipantHelper.prepareParticipants: user not defined xxxxxxxx

I cannot unsubscribe them from the UI, because they're not provided anymore.

Is there any other way to unsubscribe them than doing it directly in the 
database?

If there's no other way, how should I do it in the database?

Cheers,

J-F